Commit 6460440f authored by Kevin Wolf's avatar Kevin Wolf
Browse files

block: Allow wait_serialising_requests() at any point 



We can only have a single wait_serialising_requests() call per request
because otherwise we can run into deadlocks where requests are waiting
for each other. The same is true when wait_serialising_requests() is not
at the very beginning of a request, so that other requests can be issued
between the start of the tracking and wait_serialising_requests().

Fix this by changing wait_serialising_requests() to ignore requests that
are already (directly or indirectly) waiting for the calling request.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Reviewed-by: default avatarMax Reitz <mreitz@redhat.com>
Reviewed-by: default avatarBenoit Canet <benoit@irqsave.net>
parent 7327145f

block.c

+10 −3
Original line number Diff line number Diff line
@@ -2328,11 +2328,18 @@ static void coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self) 
                 */

                assert(qemu_coroutine_self() != req->co);



                /* If the request is already (indirectly) waiting for us, or

                 * will wait for us as soon as it wakes up, then just go on

                 * (instead of producing a deadlock in the former case). */

                if (!req->waiting_for) {

                    self->waiting_for = req;

                    qemu_co_queue_wait(&req->wait_queue);

                    self->waiting_for = NULL;

                    retry = true;

                    break;

                }

            }

        }

    } while (retry);

}

include/block/block_int.h

+2 −0
Original line number Diff line number Diff line
@@ -68,6 +68,8 @@ typedef struct BdrvTrackedRequest { 
    QLIST_ENTRY(BdrvTrackedRequest) list;

    Coroutine *co; /* owner, used for deadlock detection */

    CoQueue wait_queue; /* coroutines blocked on this request */



    struct BdrvTrackedRequest *waiting_for;

} BdrvTrackedRequest;



struct BlockDriver {